Your approach to pollution reduction relies upon a switch to lower emission vehicles and the fitting of DPF devices. Unfortunately these can be taken off, which means that there is an unknown number of vehicles in London which only comply with emissions standards on paper, rather than in reality. This potentially undermines London's attempts to reduce the impact of pollution on health. I was therefore surprised to discover that Transport for London has no plans to address this issue, or to test out new devices which can identify DPF removal in car fleets such as the taxi and private hire fleets which it regulates. Will you ask them to change their approach?